Despite improvements in durability, most expandable hoses are not suitable for use with a pressure washer. The extreme pressure (2000-3000 PSI) will overly expand the latex, likely leading to it bursting.

You can connect two expandable hoses together. There are a couple of technicalities, however. The two hoses need to have the same diameter at their opening and must have opposing male or female ends to be able to connect. If either of these issues is present, you'll have to use an adaptor.